Solved.

Fire

I'll admit, I do like fire. I mean, I'm not a pyromaniac and nor do I want to be, but I just think it's cool. But when it comes to getting stuck in a wild fire, that's a whole new story.
After school, I was trudging through the grass and rotting branches in the forest. I have to take a path through the forest in order to get to my house. I was staring at the ground when suddenly things got a little warm. I looked around and saw that no more than fourty feet away from me, my friend's house was ablaze. I looked around to find nobody outside. I did the stupid thing by dropping my backpack and I sprinted right into the house. Upon entering, I heard my friend's screams from upstairs.
"Of course, upstairs." I muttered to myself and went to the stairs. A piece of the roof fell and blocked the way I came in. I don't consider myself much of a brave, heroic person, but mess with my friends, it's over. I dashed up the stairs.
"Leo!" I called. I heard his cry for help coming from his sister's room. I went to the door and opened it, finding him and his sister Arabella hugging eachother. His sister was only a couple years younger than me. About 10 or 11. I scooped his sister up.
"Get out of here! Quickly!" I said. He ran downstairs and I followed close behind. We found no way out, so my friend took a frying pan and smashed the window. I looked at the stove and it wasn't on, so that wasn't the reason the house is on fire. We climbed out the window and he settled his shaken sister.
"What happened?" I asked him.
"I don't know. Mom and Dad are at work and they left us with a nanny, and I don't know where she is." he said.
"Ok.. Well the stove wasn't on. Maybe a failed furnace?" I asked.
"It shouldn't be on." He said.
"Ok.. What are we doing? We need to call the fire department!" I said and sprinted around the house to my bag. Leo and his sister followed. I grabbed my phone and dialed the fire department number.
After about 10 minutes, they arrived and put out the fire. They had asked us what happened and none of us knew. They recovered the nanny's burnt body. I told him that he could stay at my house until his parents got back. I'm sure they have someone else to go to in this situation.

Me, Leo, and his sister were upstairs in my room. Leo had called his mother and told him what happened. He was really shaken. Once his parents came and picked him and Arabella up, I began thinking of what would've cause the fire. The nanny's body was really burnt, so I figured she was the first thing set up in flames. But how?
Things around here are so weird and gruesome, I wouldn't be surprised if someone set her on fire. I thought about what the firemen were talking about and where they found her. They found her next to the fuse box. That was it! She must've been set on fire and she hit the fuse box creating a malfunction and the place was set on fire. That must be it.
But who did it?